Comparative approaches provide unique experimental models and a perspective of biological history of regulation of blood pressure (BP). Therefore, knowledge obtained from studying lower animal forms should be very applicable towards the understanding of the BP control system in man. The aim of the project is to define the evolution of the regulatory mechanisms of BP, in particular, the role of the renin-angiotensin (RAS) and adrenergic nervous system in primitive vertebrates. The major findings during the second year are as follows: 1) Angiotensin II caused biphasic responses in conscious chickens; initial depressor which appears to be the direct angiotensin action on the blood vessels, followed by a pressor action presumably caused by catecholamine release. 2) Resting BP of the birds is high. Both propranolol and reserpine, but not SQ 14,225, decreased BP and heart rate in conscious chickens. Plasma catecholamines increased after propranolol. 3) In aglomerular toadfish, however, SQ 14,225 decressed BP and markedly increased plasma renin activity, whereas depletion of catecholamines by 6-hydroxy-dopamine did not show effect, suggesting that RAS have a primary action in maintaining BP in fish. 4) Isolated and perfused proximal tubules from freshwater rainbow trout showed a negative transepithelial voltage (Vt) in the lumen, while a lumen-positive Vt was found in the distal tubule. the distal tubule is nearly impermeable to water, but transport C1 with the rate comparable to mammalian thick ascending limb. We plan to determine in the following year: 1) mechanism of control renin release in fowl, 2) characterization of depressor action of angiotensin with in vivo and in situ preparations, 3) role of beta adrenergic function in cardiovascular function and elevated BP in flow. We will continue to study 4) transport properties of isolated tubules from fish and effect of angiotensin on them.